The head of the Michigan health department and the state’s chief medical officer are the latest to be charged in an investigation into Flint’s lead-contaminated water.

Nick Lyon, head of the Department of Health and Human Services, was charged Wednesday with involuntary manslaughter and other crimes. He’s accused of failing to alert the public about an outbreak of Legionnaires’ disease in the Flint area, which has been linked by some experts to poor water quality in 2014-2015.

Dr. Eden Wells is charged with obstruction of justice and lying to a police officer.

The investigation led by Attorney General Bill Schuette and Genesee County Prosecutor David Leyton has already led to charges against 13 current or former government officials, including two city emergency managers appointed by Gov. Rick Snyder.

Lyon and Wells are the highest-ranking officials to be charged in the state attorney general’s investigation.

Flint started using water from the Flint River to save money in 2014 but it wasn’t treated to reduce corrosion. Lead from old plumbing leached into the water system.

Legionnaires’ is a type of pneumonia caused by bacteria that thrive in warm water and infect the lungs. People can get sick if they inhale mist or vapor, typically from cooling systems.

There were nearly 100 cases in the Flint area, including 12 deaths, in 2014 and 2015.